Tokkai 2000-164232 published by the Japanese Patent Office in 2000 discloses a humidity regulation module for a fuel cell. The humidity regulation module comprises a dry air passage disposed in an air supply channel to the air electrode (oxygen electrode) and a humid air passage disposed in a discharge channel from the air electrode. Discharge air having a high moisture content flows through the humid air passage and supplied (fresh) air having a low moisture content flows through the dry air passage. As a result, since the moisture contained in the discharge air is transferred to the supplied air, the air to be supplied to the fuel cell is humidified.